An exemplary embodiment of this application relates to an adjustable force driving nip assembly for use in a sheet handling system of, for example, a document creating apparatus. More particularly, the exemplary embodiment relates to an adjustable force driving nip assembly located in the registration areas of the sheet transport path of a document creating apparatus, such as a copier or printer. Each driving nip assembly has a plurality of individual adjustable force driving nips that are spaced transversely across the sheet transport path. Each individual driving nip has a spring-biased idler roller mounted on a pivoting cam follower with the idler roller being mated with a driven roller to form the driving nip. The normal force generated by the spring bias of the idler roller and applied to a sheet passing between the nips formed by the idler rollers and the driven rollers may be automatically adjusted in response to sheet media parameters an end user inputs into the control panel of the document creating apparatus.
In document creating apparatus, such as, for example, xerographic copiers and printers, it is increasingly important to be able to provide faster yet more accurate and reliable handling of a wide variety of image bearing sheets. Typically, the sheets are paper or plastic transparencies of various sizes, weights, and surfaces and may be subject to varying environmental conditions, such as humidity. Elimination of sheet skewing or other sheet misregistration is very important for proper imaging. In addition, sheet misregistration or misfeeding can adversely affect sheet feeding, ejection, as well as stacking and finishing of the sheets. While many document creating apparatus have adequate deskewing and side registration systems, as delineated in the prior art listed below, none have the ability to prevent sheet marking automatically for a wide range of sheet media.
Sheet transporting devices are known to have driving nips that are typically designed to provide a normal force on the paper being transported therethrough that is sufficient to provide drive forces for sheets with particular media parameters without marking the sheet. However, as substrate or sheet mass increases, the potential for slip increases as well. Normal forces in the driving nip can be increased to offset this, but the potential for marking the lighter weight paper also increases. Thus, it is the aim of the exemplary embodiment of this application to provide automatic adjustment of the normal force of the driving nips to accommodate the transport of a wide variety of sheet media used by the document creating apparatus without marking the sheets being transported.
U.S. Pat. Nos. 5,678,159 and 5,715,514 disclose dual differentially driven nips for automatic deskewing and side registration of sheets to be imaged in a printer, including the appropriate controls of the differentially driven sheet steering nips and including cooperative arrayed sheet edge position detector sensors and signal generators. As described therein, by driving two spaced apart steering nips with a speed differential to partially rotate a sheet for a brief period of time concurrently as the sheet is being driven forward by both nips, the sheet is briefly driven forward at an angle. Then the relative difference in the nip drive velocities is reversed to side shift the sheet into a desired lateral registration position as well as correcting any skew of the sheet as it entered the steering nips. Thus, the sheet exits the steering nips aligned in the process direction as well as being side registered.
U.S. Pat. No. 6,173,952 discloses a sheet handling system for correcting the skew and/or transverse position of sequential sheets moving in a process direction in a sheet transport path of a reproducing apparatus to be registered for image printing. The deskewing and/or side registration is accomplished by partially rotating the sheet with a transversely spaced pair of differentially driven sheet steering nips. The range of sheet size capabilities of this system may be increased without steering nip slippage or other problems by applying a control signal proportional to the width of the sheet to the system for automatically increasing or decreasing the transverse spacing between the pair of sheet steering nips. This is accomplished by automatically engaging only a selected pair of steering nips out of a plurality of different fixed position sheet steering nips and disengaging the others by lifting their idlers out of the sheet path with cams rotated by a stepper motor. The rotation of the cams by the stepper motor is controlled by the sheet width signal.
U.S. Patent Publication No. 20040251607 published Dec. 16, 2004 discloses a system for automatically releasing selected plural sheet feeding nip sets spaced along a sheet feeding path of a printer. Each nip has an idler roller and a driven roller. The idler rollers are rotatably mounted on common idler shafts. A selectable rotation system driven by a single low cost motor is connected to the plural idler shafts to partially rotate eccentric cams on each idler shaft to lift the idler shafts and thereby move the idler rollers away from their mating driven rollers to release all sheet feeding nips.